A known brush assembly has a brush base and a plurality of brush units. The brush base has a through hole in a central portion thereof through which a rotary shaft extends. The brush units are mounted around the through hole to engage a commutator on the shaft. Each of the brush units includes a brush, a generally U-shaped rail, and a spring mounted around the rail. The brush unit is fixed to the brush base by the rail. As shown in FIGS. 1-3, the brush base 1 forms a plurality of outer fixtures 12 for fixing closed ends 21 of the rails 2, and a plurality of pairs of inner fixtures 11 for fixing free ends 22 of the rails 2. In detail, when the rail 2 is assembled to the brush base 1, the closed end 21 of the rail 2 is engaged in a groove of the corresponding outer fixture 12, and then the two free ends 22 of the rail 2 are pushed down to squeeze protrusions 112 of the corresponding pair of inner fixtures 11 to make the inner fixtures 11 deform elastically, whereby the free ends 22 of the rail 2 can slide past the protrusions 112 and then being locked in a space between the protrusions 112 and platforms 113, with the free ends 22 of the rail 2 being disposed in grooves 111 of the inner fixtures 11.
Such fixing construction of the rail described above is applicable to a brush base which is soft and elastic, and situations of not high temperature. Since the rail 2 cannot elongate in the radial direction, the protrusions 112 of the inner fixtures 11 are easily broken or damaged by the free ends 22 of the rail 2 if the inner fixtures 11 are made of high hardiness materials, such as PPS (Polyphenylene sulfide), which results in the rail 2 being not sufficiently rigidly fixed allowing excessive movement of the brush during use. In addition, such fixing construction cannot endure high temperature, and thus is not suitable for use in a totally enclosed, high power motor.
Hence there is a desire for an improved brush assembly for an electric motor.